1. Field of the Invention
The invention, in general, relates to a cutter assembly and, more particularly, to a combination of a perforated disc and a knife for use in meat grinders or similar diminution machinery provided with feed screws or augers rotatably mounted in a pressure housing and with single or multiple-component cutter sets.
2. The Prior Art
In its simplest form, a cutter set for meat grinders is made up of a perforated disc rigidly mounted in the cutter housing of the meat grinder and of a knife associated with the perforated disc and rotatably driven by the feed auger provided with an axial stub for receiving the knife. An arrangement of a plurality of knives and perforated discs constitutes a multiple-component cutter assembly.
During rotation of the knives, their cutting edges move over the surfaces of the perforated discs to chop the material advanced against the surfaces of the perforated disc facing the interior of the housing or, in the event, the flow of the material. The perforations in the discs are fabricated in various ways and, depending upon their disposition in the surface of the disc, they participate in the acceptance and movement of the material. The reason for this is that the perforations or bores are distributed over the entire surface of a disc, arranged in different coordinates and disposed in different ways relative to the arms of the knives. The different dispositions and different pressure build-up in the raw material lead to different feed processes in individual perforations or segments of a perforated disc.
The state of the art is replete with perforated discs and rotary knives used in such cutter assemblies. The perforated discs serve not only to receive within their perforations the material being processed, but also to compact and support the material, their edges functioning as counter blades for the rotating knife to accomplish the cutting or chopping action.
To function as counter blades the perforated discs are made from tool and other high-quality steels of a Rockwell C hardness of between about 50 and about 62. Moreover, the selected material, the perforation density and the number of perforations in a given disc are of the utmost importance as regards the rate of feed of material through the disc, and they bear upon the quality of the entire cutting assembly.
Hitherto, perforated discs have been made to provide a plurality of perforations constituting bores with little resistance to material feeding, care being always taken to ensure disposition of these perforations such that they provide sharp edges relative to the surface of the disc and to provide a high-grade surface smoothness to interfere as little as possible with the feeding of the material through the perforations.
Thus, German Patent DD 277,399 relates to the problem of an optimum perforation density in a disc. As disclosed, the surface ratio between perforated and non-perforated areas is between 0.2 and 0.3, the density is between &lt;60 and 80%. The connected surface portions are said to constitute a system of secondary cutting edges, and the width of a perforated disc structured in this manner is to be in certain proportion to the diameters of the perforations. The width of perforated discs structured in this manner is to between about 0.125 to about 0.25 times the diameter of the bores.
German Patents 3,821,930 and 4,338,347 relate to the material of perforated discs relative to mechanical processing and to its matching with a given knife. In particular, German Patent 3,821,930 describes a meat grinder the perforated disc and knives of which are covered by a ceramic coating. Suitable ceramic materials are aluminum oxide (Al.sub.2 O.sub.3), zirconium oxide (ZO.sub.2), silicon carbide (SiC) or mixtures of such materials.
With a view to reducing the technical complexity of the manufacture and its costs, German patent 4,338,347 discloses a perforated disc for meat grinder cutter sets made of grey cast iron, preferably spheroidal graphite cast iron or laminar cast iron with a Rockwell C hardness between about 25 and 28.
All perforated discs hitherto known have been structured in the mentioned manner, care having always been taken to ensure the perforations are as sharpedged as possible and that the wall surfaces of the perforations were as smooth as possible for feeding the material through the disc perforations substantially without interference. This has been found to be disadvantageous, however, because the material could only be fed through the perforations, always in as straight a feed direction through the perforated disc and cutter set as possible. This does not, however, positively affect the cohesion of the material being chopped.
A further disadvantage of known knives and perforated discs is the different cutting sequences which leads to particles or grains of different sizes within the perforations of the disc and, hence, to different levels of pressures pressure in given areas of the perforated disc.